The overall objectives of the present proposal are the isolation and analysis of Suppressor-mutator (Spm) controlling elements and the molecular analysis of the Activator (Ac) controlling element. We plan to isolate the Spm controlling element by cloning genomic DNA fragments from plants that have an Spm insertion mutation at the Bronze locus. We will then undertake the isolation of the A locus with the subsequent purpose of studying the locus isolated from plants that have a variety of mutant Spm elements inserted at the locus. The purpose of these experiments is to understand the function of the element and the genetic mechanisms which regulate the developmental timing of controlling element transposition. We also plan to continue our studies on the Ac element that we have recently cloned. The objectives of these studies is to understand the function of the element and to explore its potential not only as a gene transfer vector, but also as a mutagen and gene marker in plants other than maize. We will begin by sequencing the Ac element and studying its expression in vivo. We will also develop assay systems that will facilitate its further analysis by in vitro mutagenesis. Finally, we will explore procedures for the reintroduction of the element into plant cells and plants in a functional form as a preliminary step in exploring the utility of the elements for the introduction of foreign genes.